A major national concern is the ability to dispose of wastes containing radionuclides and toxic metals in a safe manner. Large volumes of such wastes are generated by nuclear weapons production facilities, nuclear and fossil fueled power generation plants and the metal fabrication industries. Stabilizing and reducing the mass of the radionuclides and toxic metals contained in such wastes would facilitate their disposal. As used herein, stabilization means the treatment of radionuclides and toxic metals so that they are in a stable or insoluble form and lack the ability to be easily converted chemically or biologically to another soluble form. Examples of radionuclides found in such wastes include uranium, plutonium and thorium; examples of toxic metals include cadmium, cobalt, chromium, copper, lead, zinc, nickel and manganese.
Microorganisms which are ubiquitous throughout nature have long been recognized for their ability to bring about transformations of organic and inorganic compounds. Such microbial processes play a major role in the transformation and transport of radionuclides and toxic metals in nature. Radionuclides and toxic metal compounds in wastes may be present initially as soluble forms or, after disposal, they may be converted to soluble forms by chemical or microbiological processes.
The microbiological reactions include 1) oxidation/reduction, 2) change in pH and Eh which effect the valence state of the metal as well as its solubility characteristics, 3) production of sequestering agents, and 4) bioaccumulation. All of these processes can lead to attenuation or mobilization of metals in the environment.
The predominant forms of toxic metals and radionuclides found in radioactive and fossil-energy wastes can be divided into the following general categories: oxides (simple and complex oxides including ferrites), coprecipitates (metals coprecipitated with oxides of iron, aluminum), carbonate complexes, naturally occurring minerals, and organic and inorganic complexes.
Prior art techniques are known which utilize the recognized in situ microbial action on wastes to direct specific outcomes.
U.S. Pat. No. 3,923,597 to Chakrabarty, et al. describes the binding or biosorption of mercury from an aqueous waste stream by genetically engineered mercury resistant aerobic Pseudomonas species.
U.S. Pat. No. 4,468,461 to Bopp describes a use of aerobic bacteria Pseudomonas fluorescens to reduce chromate from Cr.sup.6+ to Cr.sup.3+ in which form the chromium is precipitated from aqueous waste contaminated therewith.
Union of Soviet Socialist Republic patent No. 910,815 describes the extraction of metals such as copper and zinc from ores using specific aerobic acidophilic Thiobacillus ferrooxidans.
Union of Soviet Socialist Republic patent No. 498,338 describes Aerobic bacteria Achromobacter delicatulus being used to solubilize anionic phosphorus from manganese oxide ores due to organic acids produced from metabolism of glucose and other carbon sources.
U.S. Pat. No. 3,266,889 to Duncan, et al. describes a method for extracting metals from sulfide ores using the acidophilic, aerobic bacteria Thiobacillus ferrooxidans. In this process sulfuric acid is generated due to oxidation of sulfur compounds. The sulfuric acid is primarily responsible for solubilization and extraction of metals from ores.
U.S. Pat. No. 4,861,519 to Tusa, et al. describes mass reduction of low activity nuclear power plant wastes by using anaerobic microbes to selectively degrade the organic constituents of the waste leading to the production of methane.
U.S. Pat. No. 4,885,094 to Srinivasan, et al., describes digestion of organic waste, e.g., sewage sludge, by anaerobic microorganisms.
The purpose of the present invention is to improve upon prior art techniques with a biotechnological approach to the clean-up of wastes containing toxic metals and/or radionuclides.